Semiconductor component manufacturers are constantly striving to increase the speeds of their components. Because a semiconductor component, such as a microprocessor, can contain more than a billion transistors, the focus for increasing speed has been to decrease the gate delays of the semiconductor devices that make up the semiconductor component. As a result, the gate delays have been decreased to the point that speed is now primarily limited by the propagation delay of the metallization system used to interconnect the semiconductor devices with each other and with elements external to the semiconductor component. Typically, metallization systems comprise a plurality of interconnect layers vertically separated from each other by a dielectric material and electrically coupled to each other by metal-filled vias or conductive plugs. Each layer contains metal lines, metal-filled vias, or a combination of metal lines and metal-filled vias separated by an insulating material. To decrease the signal delay through these structures, manufacturers use highly conductive metals such as copper for the primary signal conductors.
In addition to the gate delays and the metallization system, the structure of the contacts affects the speed of the semiconductor component. Contacts are metallization structures that couple the silicon portions of the semiconductor device to the metallization system. Typically, a contact comprises a layer of metal silicide and a conductive material formed on the metal silicide layer. The metal silicide layer is formed by depositing a refractory metal such as titanium on the semiconductor substrate and heating the metal and semiconductor substrate to form the metal silicide. A drawback with this approach is that a high temperature anneal is needed to achieve sufficient titanium-silicon intermixing to form a metal-silicide layer having an acceptably low resistance. Another drawback is that formation of the silicide layer consumes silicon from the semiconductor substrate, which may increase the resistance of the semiconductor material near the contact structure.
Accordingly, what is needed is a contact structure for use in a semiconductor component and a method for manufacturing the contact structure.